The aim is to conclude a free-trade pact by the end of the year that includes the United States, Japan and other major trading nations on both sides of the Pacific Ocean. The talks don’t include China, which sees the TPP as an American-led attempt to curb Beijing’s influence in its own backyard — something the U.S. has been at pains to deny.

The agreement aims to go beyond tariff reductions to address issues ranging from government procurement to intellectual property rights. Negotiations received a major boost this summer when Japanese Prime Minister Shinzo Abe pushed past domestic opposition to bring the world’s third-largest economy to the table – meaning the 12 countries in the negotiating room will comprise a massive 40% of the global economy.

Establishing a free-trade zone that includes the U.S., Australia, Japan, Malaysia, New Zealand, Singapore, Brunei, Vietnam, Canada, Mexico and Chile would be a major success for the Obama administration’s goal of extending U.S. influence in Asia-Pacific. The push comes as the U.S. has stationed Marines in Australia and boosted training exercises with the Philippines just as China’s aggressive territorial claims in the South China Sea have inflamed relations with many of its neighbors in Southeast Asia.

But reaching a deal, especially in a matter of months, won’t be easy: This week’s round of negotiations will already be the nineteenth since 2010. And despite Japan’s decision to join the talks, serious disagreements remain over Tokyo’s dogged defense of its agricultural sector.

What’s more, if the incentive for a deal is indeed to contain China, it will run up against the fact that China is negotiating its own free-trade agreements with Japan, South Korea and Australia – to complement its FTA’s with New Zealand and the 10-member Association of Southeast Asian Nations — and has displaced the U.S. as the most important trading partner for much of Asia-Pacific. Apprehensions that the TPP is an anti-Chinese plot could sour Beijing’s attitude toward Washington and even reduce the odds of finding conciliatory solutions in the South China Sea.

Second, Mr. Abe has proven his ability to cut through many of the Gordian knots that have deadlocked Japanese policy for years. His support for the TPP suggests a newfound understanding that freer trade will be crucial for Japan’s economy going forward.

About Real Time Economics

Real Time Economics offers exclusive news, analysis and commentary on the U.S. and global economy, central bank policy and economics. Send news items, comments and questions to the editors and reporters below or email realtimeeconomics@wsj.com.